As default behavior of the QGraphicsItems "Z Values", independent Top-Level QGraphicsItems apparently can't be drawn between distinct "Z" layers of the nested QGrahpicsItem children of other Top-Level QGraphicsItems.

The Qt 4.6.3 example below shows these QGraphicsItems:

1. Top-Level QGraphicsRectItem .. Z = 1.0
2. ... Child QGraphicsTextItem .. Z = 3.0
3. Top-Level QGraphicsLineItem .. Z = 2.0

Notice that the Line Item obscures the Text Item, even though the Text Item has a higher Z-Value (but does not have the same parent QGraphicsItem). [Qt 4.6.3, 12-2010].

QUESTION: Are there any QGraphicsScene or QGraphicsItem configuration properties which can modify this behavior?

EnigmaActual.gifEnigma3D.gif
Images are also available here. See also screenshot of problem in our application (RiverWare).

Qt Code: 
  1. // File: ZProblem.cpp
  2. //
  3. // QGraphicsItems:
  4. //   (1) Top-Level QGraphicsRectItem  .. Z = 1.0
  5. //   (2) ... Child QGraphicsTextItem  .. Z = 3.0
  6. //   (3) Top-Level QGraphicsLineItem  .. Z = 2.0
  7. //
  8. // Notice that the Line Item obscures the Text Item, even though the
  9. // Text Item has a higher Z-Value (but does not have the same parent 
  10. // QGraphicsItem). [Qt 4.6.3, 12-2010].
  11.  
  12. #include <QApplication>
  13. #include <QGraphicsScene>
  14. #include <QGraphicsView>
  15. #include <QGraphicsLineItem>
  16. #include <QGraphicsRectItem>
  17. #include <QGraphicsTextItem>
  18. #include <ostream>
  19.  
  20. int main(int argc, char** argv)
  21. {
  22.    QApplication app (argc, argv);
  23.    QGraphicsScene myScene;
  24.  
  25.    // **************************************************
  26.    // ***  Create Top-Level Rectangle QGraphicsItem  ***
  27.    // **************************************************
  28.  
  29.    const int RectWidth  (300.0);
  30.    const int RectHeight (220.0);
  31.  
  33.       -0.5 * RectWidth, -0.5 * RectHeight, RectWidth, RectHeight);
  34.  
  35.    rectItem->setBrush (QColor (0x66, 0xCC, 0xCC));  // blue-green
  36.    rectItem->setPen (QColor (Qt::black));
  37.    rectItem->setFlags (QGraphicsItem::ItemIsMovable);
  38.  
  39.    rectItem->setZValue (1.0);    // *** Z VALUE 1.0, Top-Level Item ***
  40.    rectItem->setToolTip ("Rectangle: Z = 1.0");
  41.  
  42.    myScene.addItem (rectItem);
  43.  
  44.    // *****************************************
  45.    // ***  Create Child Text QGraphicsItem  ***
  46.    // *****************************************
  47.  
  48.    QGraphicsTextItem* childTextItem =
  49.       new QGraphicsTextItem ("ENIGMA", rectItem);
  50.  
  51.    QFont textFont;  // application default
  52.    textFont.setPixelSize (75);
  53.    textFont.setWeight (QFont::Black);
  54.    childTextItem->setFont (textFont);
  55.  
  56.    childTextItem->setZValue (3.0);  // *** Z VALUE 3.0, Child Item ***
  57.    childTextItem->setToolTip ("Child Text: Z = 3.0");
  58.  
  59.    const QRectF childRect = childTextItem->boundingRect();
  60.    childTextItem->setPos (-0.5 * childRect.width(), 
  61.                           -0.5 * childRect.height());
  62.  
  63.    // *********************************************
  64.    // ***  Create Top-Level Line QGraphicsItem  ***
  65.    // *********************************************
  66.  
  68.       -0.6 * RectWidth, 0.0, 0.6 * RectWidth, 0.0);
  69.  
  70.    QPen linePen = QPen (QColor (0xFF, 0x66, 0x66));  // red
  71.    linePen.setCapStyle (Qt::RoundCap);
  72.    linePen.setWidth (20);
  73.    lineItem->setPen (linePen);
  74.    lineItem->setFlags (QGraphicsItem::ItemIsMovable);
  75.  
  76.    lineItem->setZValue (2.0);  // *** Z VALUE 2.0, Top-Level Item ***
  77.    lineItem->setToolTip ("Line: Z = 2.0");
  78.  
  79.    myScene.addItem (lineItem);
  80.  
  81.    // ******************************
  82.    // ***  Create QGraphicsView  ***
  83.    // ******************************
  84.  
  85.    QGraphicsView myView (&myScene);
  86.    myView.setCaption ("Test QGraphicsItems Z-Values");
  87.    myView.resize (3.0 * RectWidth, 3.0 * RectHeight);
  88.    myView.show();
  89.  
  90.    return app.exec();
  91. }
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Thank you in advance,
Phil Weinstein, CADSWES
University of Colorado at Boulder, USA